Help with a formula not working - New starter

Hello, just starting with Monday.

I am trying to build a board (is that the right terminology?) that will help me with budgeting projects.

My creative business has multiple roles, creative director, senior creative, creative, junior creative - for example. Each role has a different hourly rate associated with the role.

Right now I’m using a label column for all the different roles. And I’ve figured out the formula to update the next column ‘Rate PH’ with the appropriate figure depending on the role selected. (Well the AI did).

The next column is a number column for ‘Hours’, that I update manually.

But when I set a formula in the next column ‘Rate total’ to read the automated rate in ‘Rate PH’ and multiply that by ‘Hours’. {Rate PH} * {Hours} …

It doesn’t work. It says - one of the parameters is invalid?

Any help would be gratefully received. Thanks